As winters here I wanted a small project that can be done in comfort of a warm dining room! I want to make a led bar graph rpm counter so went looking for a circuit diagram which would do the required.Below is the clearest simplest I could find but has way more led's than I want to use. Just want to have 6 green, 2 yellow, one red, giving 9k rpm in total. I have a load of these leds that I was going to use set into an arced housing around a centralised speedoSo......Can anyone alter the diagram below or has a diagram that will do what I want Diagram deleted so as not to confuse

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Last edited by warren3200gt on Wed Dec 06, 2017 9:31 am, edited 1 time in total.

Being an electronic numpty, how? I can build from a diagram but know sweet FA about what's actually going on in the circuit. Then its fingers crossed if it works. If it didn't I wouldn't know why or how to fix it!

Having watched his video can you not just connect your leds to the outputs that you want (relative to rpm) and leave the others empty. As his circuit leaves the previous leds lit I'm assuming this will stay the same until the circuit passes over the empty output(s) until it gets to the next led.

I don't know if that would work Gus. I don't know if the driver needs something (LED?) on every outlet to work or if you skip one the next in the sequence will work?I was hoping someone could tell me or re draw that diagram to just one driver as Zedhead suggests. The LM2917 bit is the bit I don't understand. Would it work if I just not do the C4, R2, DZ1 C6,C7, and R5 wires? leaving terminal 2 & 3 on the LM2917 empty? which would isolate it to one driver.

warren3200gt wrote:I don't know if that would work Gus. I don't know if the driver needs something (LED?) on every outlet to work or if you skip one the next in the sequence will work?I was hoping someone could tell me or re draw that diagram to just one driver as Zedhead suggests. The LM2917 bit is the bit I don't understand. Would it work if I just not do the C4, R2, DZ1 C6,C7, and R5 wires? leaving terminal 2 & 3 on the LM2917 empty? which would isolate it to one driver.

Ok thanks for that, So bearing in mind wasted spark it should read one pulse per one rev. Ie it wont read twice or half the desired amount?So from a syncing revs to leds, the only way to do it would be add the leds when the revs are at the desired amount. Ie with the engine running at 1k add the led to the last outlet that illuminates it. Then again at 2k etc, etc?What I was hoping to achieve was 1 led at 1k, 2 at 2k, 3 at 3k etc. Or is there way of adding in a variable that i could adjust to achieve the desired effect?

Gary, what I'm trying to achieve is an arc of 9 leds. At 1k rpm 1 led is lit, at 2k rpm 2 are lit, at 3k rpm 3 are lit etc. The only way of doing that using the circuit below would be to build it, stick it on the bike, run the bike at 1k and test which driver outputs give current, again at 2k rpm and test, again at 3k rpm and test. Then add leds to the relevant driver out puts. I was wondering if I could add in a control mechanism so that I could use one driver, add leds to all the outputs, start the engine and "turn the knob" on the control mechanism to sync the lit leds to the engine rpm.? Some sort of variable resistor or something and where to put it in the circuit?